1. Field of the Invention
The present invention relates to a biaxially stretched polyester film and a method for producing the biaxially stretched polyester film, and an optical sheet.
2. Description of the Related Art
In the related art, it has been known that a biaxially stretched polyester film, in particular, a biaxially stretched film of polyethylene terephthalate or polyethylene naphthalate has excellent mechanical properties, heat resistance, and chemical resistance. The biaxially stretched polyester film has been widely used as a material of a magnetic tape, a ferromagnetic thin film tape, a photographic film, a film for package, a film for an electronic member, an electric insulating film, a film for a metal laminate, a film bonded to a glass surface, such as a glass display film, a protective film for various members, and the like.
Recently, the biaxially stretched polyester film has been generally used, in particular, in various optical films, and has been used in various applications of a base film such as a prism sheet, a light diffusing sheet, a reflection plate, and a touch panel of a member of a liquid crystal display device (LCD), a base film for preventing reflection, a base film for preventing display explosion, a film for a plasma display panel (PDP) filter, and the like.
In order to be suitably applied to such an optical film, it is necessary that the biaxially stretched polyester film has transparency, and the biaxially stretched polyester film has excellent adhesion between the adjacent materials (for example, coating layers), durability in which a color is not changed to a yellow color or the like due to heating at the time of molding or aging, and the like.
In JP1989-185355A (JP-H01-185355), a polyester composition containing antimony metal particles having a small size in which the long diameter is greater than or equal to 0.01 μm and less than or equal to 1 μm is disclosed as a technology relevant to the above circumstances.
In addition, in JP5055661B, a producing method is disclosed in which an antimony compound is used as a polycondensation catalyst performing a polycondensation reaction between a dicarboxylic acid component and a diol component, and the timing of adding each of a magnesium compound and a phosphorus compound is adjusted during the polycondensation reaction, and thus polyester for a film is produced. It is disclosed that in the polyester for a film produced in the producing method described above, the amount of antimony in the residues on a membrane filter having an average pore diameter of 0.1 μm after a solution in which parachlorophenol and tetrachloroethane are dissolved in a solvent at a ratio of 75:25 (a weight ratio) is filtered by the membrane filter is less than or equal to 1 mg/1 kg of polyester. Further, it is disclosed that a biaxially stretched polyester film prepared by using the polyester for a film produced in the producing method described above has excellent transparency.
Further, in JP4023219B, an easily adhesive polyester film for a prism lens sheet is disclosed in which an easily adhesive layer containing a resin such as a polyester resin or a polyurethane resin as a main component is disposed on at least one surface of a biaxially aligned polyester film having a thickness of 50 μm to 300 μm which contains an antimony compound, an alkali earth metal compound, and a phosphorus compound.